Solar Collector and Mounting Bracket

ABSTRACT

A solar collector with a rectangular frame ( 1 ), preferably made of extruded or rollformed metal, containing an absorber plate ( 3 ), an insulating layer ( 2 ) beneath the absorber plate ( 3 ), and a cover pane ( 4 ) spaced above the absorber ( 3 ). Absorber tubing ( 3   b   .3   c ) is attached to the rear side of the absorber plate. The absorber ( 3 ) is secured to the frame ( 1 ) by mounting brackets ( 11   a   ,11   b ) that engage the absorber tubing ( 3   b   ,3   c ) and allow for substantially unhindered thermal expansion and contraction of the absorber. The collector can be integrated or roof mounted on a pitched roof, or may be installed on a flat roof by means of a mounting frame.

The present invention relates to solar collectors and mounting brackets, in particular solar collectors that include a rectangular frame, preferably made of extruded or rollformed metal, containing an absorber plate, an insulating layer beneath the absorber plate, and a cover pane spaced above the absorber. Absorber tubing is attached to the rear side of the absorber plate. The collectors can be integrated or roof mounted on a pitched roof, or may be installed on a flat roof by means of a mounting frame.

BACKGROUND ART

WO 2004/111550 discloses such a type of solar collector. The absorber is simply inserted in the frame or another housing. The absorber is held in place by the connection of the absorber tubes to the frame, but it is also known to hold the absorber in place by imbedding the absorber in the insulation material.

Neither method for securing the absorber is ideal. A stiff connection between the absorber tubes and the frame cannot provide for the required flexibility, which is needed to deal with the large temperature variations and the consequent expansions and contractions in order to avoid tensions and damages.

Absorbers that are simply placed on the insulation layer, e.g. stone wool, and have flexible connections between the absorber tubes and the frame, are known to have problems with the absorber plate getting displaced during transport or during mounting of the solar collector on a roof or the like.

EP 1 243 874 discloses a type of solar collector in which the absorber is secured to the frame by resilient fasteners. The resilient fasteners reduce the risk of displacement during transport or mounting, but do not quite eliminate the problem. Further, this solution requires that several mounting tubes are added to the absorber construction to provide an engagement point for the resilient fasteners.

DISCLOSURE OF THE INVENTION

On this background, it is an object of the present invention to provide a solar collector in which the absorber is secured in a reliable and flexible manner. This object is achieved in accordance with claim 1 by providing solar collector comprising a frame, preferably made of extruded or rollformed metal, an absorber plate, absorber tubing secured to the rear side of the absorber plate, an insulating layer beneath the absorber plate, a cover pane spaced above the absorber, four or more mounting brackets for connecting the absorber with the frame, said mounting brackets engage the absorber tubing, whereby a first mounting bracket engages the absorber tubing in a manner that does not allow any substantial displacement between the first bracket and said absorber tubing, a second mounting bracket engages the absorber tubing in a manner that allows displacement between the second bracket and said absorber tubing only in a first direction in the plane of the absorber plate to allow for thermal expansion and contraction of the absorber plate in said first direction, a third mounting bracket engages the absorber tubing in a manner that allows displacement between the third bracket and said absorber tubing only in a second direction in the plane of the absorber plate that is substantially transverse to the first direction to allow for thermal expansion and contraction of the absorber plate in said second direction, and a fourth mounting bracket engages the absorber tubing in a manner that allows displacement between the fourth bracket and said absorber tubing in both the first and second direction to allow for thermal expansion and contraction of the absorber plate in said first and second direction.

The first mounting bracket fixes the position of the absorber to the frame, and the risk of the absorber plate getting displaced during transport or mounting of the solar collector is substantially eliminated. The other mounting brackets allow a substantially unhindered thermal expansion of the absorber plate, and this there amount of tension an stress that could otherwise be caused during the large day/night summer/winter and stagnation temperatures fluctuations to which a solar collectors are exposed.

The mounting brackets may be rectangularly spaced apart, and the absorber tubing preferably includes two parallel tubes with a preferably larger diameter that are interconnected by a plurality of preferably lesser diameter tubes extending between the large diameter tubes in a direction substantially transverse to the large diameter tubes. Preferably, the larger diameter tubes extend in the first direction, whereas the lesser diameter tubes extend in the second direction.

The first mounting bracket and the fourth mounting bracket are preferably disposed diagonally opposite to one another. The second mounting bracket and the third mounting bracket are preferably disposed diagonally opposite to one another.

The first mounting bracket may engage both a tube section that extends in the first direction and a tube section that extends in the second direction, preferably there where the two tubes are connected to one another.

The second mounting bracket may slidably engage a tube section that extends in the first direction to allow for displacement between said tube section and the second mounting bracket in the first direction.

The third mounting bracket may slidably engage a tube section that extends in the second direction and loosely engages a tube section that extends in the first direction to allow for displacement between said tube sections and the third bracket in the second direction.

The fourth mounting bracket may loosely- and slidably engage a tube section that extends in the first direction or in the second direction to allow for displacement between said tube section and the fourth bracket in the first and second direction.

Preferably, the four or more mounting brackets are substantially identical to one another.

It is yet another object of the present invention to provide a mounting bracket for use in a solar collector that assets in overcoming the problems describer above.

This object is achieved in accordance with claim 11 by providing mounting bracket for use in a solar collector for engaging one or more tube sections, the mounting bracket comprising two tube engaging members that can be fixed to engage a tube section in at least two positions, a first position in which the tube section is slidably engaged and a second position in which the tube section is loosely engaged to allow displacement between the tube section and the mounting bracket in a direction transverse to the tube section axis.

At least one of said tube engaging members can be forked so as to embrace a second tube section that extends transversely from the first tube section. This allows the bracket to engage the tubing at a connection point between two tube sections.

The mounting bracket may further include a base plate for attaching the mounting bracket to the frame of the solar collector, wherein said base plate is provided with three or more frame facing protrusions to minimize the contact area between the frame and the base plate. By reducing the contact area the heat loss at the connection between the mounting bracket and the frame is minimized. Through going bores in the base plate may coincide with the protrusions, so that fasteners such a pop-rivets or bolts and nuts can be applied there though and through corresponding bores in the frame.

The base plate and a first of the tube engaging members are preferably integrally connected to one another by a connecting part that is at an angle with the base plate and the second tube engaging member being securable relative to the first tube engaging member. The connecting part may comprise a substantially flat plate section, and at least a part of the oppositely disposed free edges of the flat plate section can be bent over to reinforce the mounting bracket. The free edge may be bent over to obtain a substantially U-shaped cross-section in which a flat plate part of the second tube engaging member is slidably received.

The flat plate section that is integral with the first tube engaging member can be provided with one through going bore and the flat plate part of the second tube engaging member can be provided with two through going bores that overlap with the through going bore of the flat plate section in two distinct positions, whereby the tube engaging members slidably engage the tube section in one of the two distinct positions and the tube engaging members loosely engage the tube section in the other of the two distinct positions. A pop rivet, bolt or similar fastener can be received in the through going bores to fasten the second tube engaging member in either of the two distinct positions.

The tube engaging members are preferably at least partially curved with a radius equal to or slightly larger than the tube section to be engaged.

At least a part of the mounting bracket can be made of a material with a relatively low thermal conductivity, such as stainless steel, to reduce heat loss via the mounting bracket to the frame.

Further objects, features, advantages and properties of the solar collector and mounting bracket according to the invention will become apparent from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which:

FIG. 1 is a cutaway perspective view of a solar collector according to the invention,

FIGS. 2 a to 2 c are partial cross-sectional views of the solar collector of FIG. 1 at different temperatures,

FIG. 3 is a cross sectional view through the collector in the plane of the absorber plate, illustrating mounting brackets holding the absorber tubing,

FIGS. 4 a and 4 b are cross sectional views transverse to the plane of the absorber to illustrate a detail of the engagement between the mounting bracket and the absorber tubing, and

FIGS. 5 a and 5 b are perspective views showing the mounting bracket in detail.

DETAILED DESCRIPTION

A preferred embodiment of the invention will be described specifically with reference to a flat plate collector assembly although it is understood that other absorber types may be employed with a minimum change in construction.

FIG. 1 shows by way of illustrative example a flat plate solar energy collector. Seen in cutaway perspective view of FIG. 1 the solar collector has a frame 1, an insulation layer 2, an absorber plate 3 and a cover pane 4. The frame, the insulation layer and the cover pane form a case with an enclosure. The enclosure is used to provide support for the absorber, and to protect the collector from heat loss due to wind, plus the important function of keeping moisture from rain, snow and dew out of the collector.

The insulation layer 2 is made of a rigid foam urethane (PUR) or polyisocyanurate (PIR). These materials have an excellent insulation value per unit of thickness and are easy to handle because they are very light. They have also a higher compression resistance than e.g. mineral wool based insulation materials.

The upper surface of the insulation layer 2 is covered with a reflective silver foil and provided with a recess sized to be able to receive the absorber 3. The absorber 3 is received in the in the recess and except for its upper side surrounded by the insulation layer 2.

As shown in FIG. 2 a the absorber comprises an absorber plate 3 a and an absorber tubing 3 b that channels the medium, typically water, used to transport the collected thermal energy. The absorber plate 3 a and the copper tubing 3 b may suitably consist of steel, copper or aluminum sheet or tubing, respectively.

The absorber plate 3 a is provided with a semi-selective or a selective coating to improve the heat absorbing capacity of the absorber plate 3 a.

The solar collector may also be provided with a backsheet 5 to protect the insulation layer 2 from weather influences and to increase the rigidity of the construction. The backsheet is suitably formed by a plastic sheet or film material weaker than the frame material, e.g. polypropylene sheet or aluminum foil. A backsheet can be altogether avoided if the bottom side of the insulation layer is coated.

The frame 1 comprises four side panels that are part of one rollformed sheet material profile. The sheet material is suitably made of sheet metal, preferably pre-painted aluminum.

The side panels 1 are substantially shaped as a U-profile with an upper inwardly directed latch 1 a and a lower inwardly directed latch 1 b. The upper latch 1 a is provided with an upstanding rim 1 c.

The details of the frame construction and the type of insulation material are however not crucial for the present invention, and the frame could alternatively be made from extruded metal (aluminum) or from wood and a back sheet. A layer of mineral wool can be sued instead of rigid foam as insulation material.

The upstanding rim 1 c acts as a spacer that supports the cover pane 4 and maintains a distance between the upper surface of latch 1 a and the bottom surface of the cover pane 4 during fitting of the cover pane. A continuous EPDM neoprene gasket 7 is placed on the upstanding rims 1 c. The gasket 7 is in sealing abutment with a peripheral zone of the bottom surface of the cover pane 4 to form a moisture barrier protecting the enclosure and to insulate the cover pane 4 thermally from the side panels 1.

The gasket is provided on its outwardly facing side with a flexible dam 7 a. The flexible dam 7 a is arranged to define a hollow space between the rim and the dam itself. The hollow space allows the flexible dam to move unhindered. The gasket is provided on its inwardly facing side with a flap 7 b extending over the insulation layer and under the absorber 3. The flap protects the silver foil and the insulation layer from the sides of the absorber plate 3 a.

When the gasket has been placed on the rim 1 c, the cover pane 4 is placed on top of the gasket 7 and the space between the upper side of the latch 1 a and the bottom surface of the cover pane 4 is filled with a flexible adhesive sealant such as a silicone based sealant in liquid form. The flexible dam 7 a serves as a barrier preventing the liquid flexible adhesive sealant from entering the cavity when it is applied.

When the sealant has cured it forms a flexible layer that securely attaches the cover pane 4 to the side panels.

The layer of flexible adhesive sealant also forms a second moisture barrier protecting the enclosure. The enclosure is thus protected from moisture by a two-stage barrier, thus, reducing the likeliness of leakage significantly.

The layer of flexible adhesive sealant attaches the cover pane 4 to the side panels so that the cover pane 4 becomes an integral bearing part of the construction that contributes to the overall stability and stiffness of the solar collector. There is therefore no need for capstrips and thus there is no risk of water or snow to remain caught at the transition between the cover pane and the capstrip.

FIG. 2 a illustrates the cross-section of the solar collector at room temperature. Since this is the temperature at which the cover pane was fitted to the frame there are no discrepancies in length between the aluminum frame and the tempered glass cover pane.

FIG. 2 b illustrates the cross-section of the solar collector at a high temperature such as may e.g. occur during stagnation, i.e. when the heat transporting medium is not flowing so that the heat is not transported away. The cover pane has expanded more than the frame with the temperature raise. The difference in length is compensated for by an outwardly directed shear deformation of the layer of flexible adhesive sealant 8.

FIG. 2 c illustrates the cross-section of the solar collector at a low temperature such as may e.g. occur in a cold winter night. The cover pane has contracted more than the frame with the temperature fall. The difference in length is compensated for by an inwardly directed shear deformation of the layer of flexible adhesive sealant 8.

Flexible adhesive sealants such as silicon based sealant can well endure such deformation and still maintain good adhesion to the cover pane and the frame both at low and high temperatures. Because of the low elasticity modus of the flexible adhesive sealant the shear forces acting on the cover pane and the frame are negligible.

As shown in FIG. 3, the absorber tubing includes two horizontally (horizontal as in FIG. 3) directed tubes 3 c with a larger diameter that are interconnected by a plurality of vertically (vertical as in FIG. 3) directed lesser diameter tubes 3 b extending between the large diameter tubes in a direction substantially transverse to the large diameter tubes 3 c.

Although not shown, all tubing 3 b and 3 c may be of equal diameter.

The lower (low as in FIG. 3) of the two larger diameter tubes 3 c is connected via a section of flexible tubing 9 a to a bracket 10 a that is secured to the frame 1 and includes a conduit (not shown) extending to the outside of the frame 1 for connection to external tubing or a juxtaposed collector (not shown).

The higher (high as in FIG. 3) of the two larger tubes 3 c is connected via a section of flexible tubing 9 b to a bracket lob that is secured the frame 1 and includes a conduit (not shown) extending to the outside of the frame 1 for connection to external tubing or a juxtaposed collector.

The flexible tubing sections 9 a and 9 b ensure that the absorber plate 3 a and absorber tubing 3 c can thermally expand and contract without any tension building up at the connection between the absorber tubing 3 b,3 c and the frame 1.

Four mounting brackets 11 a,11 b,11 c,11 d support the absorber 3. These four mounting brackets are identical in construction, but can engage the absorber tubing in four different ways. The mounting brackets 11 a,11 b,11 c,11 d are rectangularly spaced apart and extend from the frame 1 to engage the absorber tubing 3 b,3 c. The mounting brackets 11 a-11 d are configured to be able to engage the larger diameter tubing 3 c either slidably, thereby allowing displacement between the larger diameter tubing 3 c and the mounting bracket in the direction of the tube axis, or loosely, thereby allowing both a limited displacement between the tube and the mounting bracket transversely to the tube axis and unlimited displacement in the direction of the tube axis. The brackets are configured to be able to engage simultaneously a larger diameter tube either slidably or loosely and a lesser diameter tube slidably at a point where the two tube types are connected to one another at substantially right angles. The engagement structure of the mounting bracket will be described in more detail further below with.

The first mounting bracket 11 a engages the absorber tubing in the left lower corner (left and lower as in FIG. 3) at a point where the leftmost lesser diameter tube 3 b connects to the lower larger diameter tube 3 c. The first mounting bracket engages both the large diameter tube 3 c and the lesser diameter tube 3 b, thereby ensuring that the absorber 3 cannot be displaced relative to the frame 1.

The second mounting bracket 11 b engages the absorber tubing in the right lower corner (right and lower as in FIG. 3), and only engages the lower larger diameter tube 3 c in a slidable manner so to allow for movement of the lower tube 3 c relative to the second bracket 11 b in the direction of arrow X. Thus, thermal expansion of the absorber 3 in the direction of arrow X can take place substantially unhindered by the connection between the frame 1 and the absorber 3 formed by the second mounting bracket 11 b.

The third mounting bracket 11 c engages the absorber tubing in the upper left corner (upper and left as in FIG. 3), and both engages the upper larger diameter tube 3 c and the left first lesser diameter tube 3 b. The third bracket 11 c engages the leftmost lesser diameter tube 3 b in a slidable manner (slidable in the direction of the tube axis, i.e. in the direction of arrow Y). The third bracket loosely engages the upper tube 3 c to so as to allow for a limited amount of movement of the upper tube 3 c relative to the third bracket in the direction of arrow Y. Thus, thermal expansion of the absorber 3 in the direction of arrow Y can take place substantially unhindered by the connection between the frame 1 and the absorber 3 formed by the third mounting bracket 11 c.

The fourth mounting bracket 11 d engages the absorber tubing in the upper right corner (upper and right as in FIG. 3). Only the upper larger diameter tube 3 c is engaged loosely by the fourth third bracket 11 d, thereby allowing displacement of the absorber in the direction of both the X and Y arrow. Thus, thermal expansion of the left part of the absorber 3 in the direction of arrow Y and in the direction of arrow Y can take place substantially unhindered by the connection between the frame 1 and the absorber 3 formed by the fourth mounting bracket 11 d.

FIG. 4 a shows a cross-sectional view through the first mounting bracket 11 a in a plane at right angles with the tube axis of the large diameter tubes 3 c. The mounting bracket 11 a is secured with a base plate 15 to the frame 1. The base plate 15 is at a right angle with a connecting part 16 that further extends into a curved first tube engaging member 12. The mounting bracket 11 a includes further a second curved tube engaging member 13. The second tube engaging member 13 includes a flat plate part 14 that is secured to the connecting part 16. The second tube engaging member can be secured in a two positions to obtain the above described slidable or loose engagement. In FIG. 4 a the second tube engagement member is in the position that gives a slidable engagement. The first tube engagement member 12 is forked and the lesser diameter tubing 3 a is embraced by the fingers of the fork.

FIG. 4 b shows a cross-sectional view through the third mounting bracket 11 c in a plane at right angles with the tube axis of the large diameter tubes 3 c. The third mounting bracket 11 c is identical to the first mounting bracket 11 a, except that the second tube engaging member 13 is secured in the position for engaging the larger diameter tube 3 c in a loose manner.

FIG. 5 a shows the mounting bracket 11 a-11 d in a perspective view with the second tube engaging member in the slidable engagement position. FIG. 5 b shows the mounting bracket 11 a-11 d in a perspective view with the second tube engaging member in the loose engagement position. These Figs. show the recess 22 in the forked first tube engaging member in which a lesser diameter tube 3 b can be received. The base plate 15 is provided with three frame facing protrusions 19 to minimize the contact area between the frame 1 and the base plate 15. By reducing the contact area the heat loss at the connection between the mounting bracket 11 a-11 d and the frame 11 is minimized. Through going bores in the base plate 15 coincide with the protrusions, and fasteners such a pop-rivets or bolts and nuts are applied there though and through corresponding bores in the frame 1 to fasten the mounting bracket 11 a-11 d to the frame 1.

The connecting part 16 includes substantially flat plate section 21, with oppositely disposed bend over free edges 17 that serve to reinforce the mounting bracket 11 a-11 d. The free edges 17 create a U-shaped cross-section in which the flat plate part 14 of the second tube engaging member 13 is slidably received.

The flat plate section 21 is provided with one through going bore (cannot be seen in the Figs.) and the flat plate part 14 of the second tube engaging member 13 is provided with two through going bores 18 that overlap with the through going bore of the flat plate section 21 in two distinct positions. The tube engaging members 12,13 slidably engage the larger diameter tube 3 c in one of the two distinct positions and the tube engaging members loosely 12, 13 engage the larger diameter tube 3 c in the other of the two distinct positions. A pop rivet, bolt or similar fastener is fitted in the through going bores 18 to fasten the second tube engaging member 13 in either of the two distinct positions.

The tube engaging members 12,13 are at least partially curved with a radius equal to or slightly larger than the larger diameter tubes 3 c. The mounting brackets 11 a-11 d, or at least a part thereof, are made of stainless steel, or other suitable material with a relatively low thermal conductivity to reduce heat loss via the mounting bracket to the frame 1.

The same mounting bracket 11 a-d is used to engage the absorber tubing in different ways:

-   -   The mounting bracket can fork or slide.     -   In addition it can be secured (pop riveted) in a closed or open         situation for sliding and loose engagement with the absorber         tubing.

Very large absorbers can be supported by 6, 8 or mere brackets, that engage the absorber tubing with an individually determined amount of freedom in displacement between the mounting bracket and the absorber tubing in accordance with the particular requirement at the point of engagement.

Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention. 

1. A solar collector comprising: a frame (1), preferably made of extruded or rollformed metal, an absorber plate (3 a), absorber tubing (3 b) secured to the rear side of the absorber plate, an insulating layer (2) beneath the absorber plate, a cover pane (4) spaced above the absorber, four or more mounting brackets (11 a,11 b,11 c,11 d) for connecting the absorber (3) with the frame (4), said mounting brackets engage the absorber tubing (3 b), whereby a first mounting bracket (11 a) engages the absorber tubing (3 b) in a manner that does not allow any displacement between the first bracket and said absorber tubing, a second mounting bracket (11 b) engages the absorber tubing (3 b) in a manner that allows displacement between the second bracket and said absorber tubing only in a first direction in the plane of the absorber plate to allow for thermal expansion and contraction of the absorber plate (3 a) in said first direction, a third mounting bracket (11 c) engages the absorber tubing (3 b) in a manner that allows displacement between the third bracket and said absorber tubing only in a second direction in the plane of the absorber plate (3 a) that is substantially transverse to the first direction to allow for thermal expansion and contraction of the absorber plate in said second direction, and a fourth mounting bracket (11 d) engages the absorber tubing (3 b) in a manner that allows displacement between the fourth bracket and said absorber tubing in both the first and second direction to allow for thermal expansion and contraction of the absorber plate (3 a) in said first and second direction.
 2. A solar collector according to claim 1, wherein the mounting brackets (11 a,11 b,11 c,11 d) are rectangularly spaced apart.
 3. A solar collector according to claim 1, wherein the first mounting bracket (11 a) and the fourth mounting bracket (11 d) are disposed diagonally opposite to one another.
 4. A solar collector according to claim 3, wherein the second mounting bracket (11 b) and the third mounting bracket (11 c) are disposed diagonally opposite to one another.
 5. A solar collector according to claim 1, wherein the absorber tubing (3 b) includes tube sections that extend in the first direction and tube sections that extend in the second direction.
 6. A solar collector according to claim 5, wherein said first mounting bracket (11 a) engages both a tube section that extends in the first direction and a tube section that extends in the second direction.
 7. A solar collector according to claim 1, wherein said second mounting bracket (11 b) slidably engages a tube section that extends in the first direction to allow for displacement between said tube section and the second mounting bracket in the first direction.
 8. A solar collector according to claim 1, wherein said third mounting bracket (11 c) slidably engages a tube section that extends in the second direction and loosely engages a tube section that extends in the first direction to allow for displacement between said tube sections and the third bracket in the second direction.
 9. A solar collector according to claim 1, wherein said fourth mounting bracket (11 d) loosely- and slidably engages a tube section that extends in the first direction or in the second direction to allow for displacement between said tube section and the fourth bracket in the first and second direction.
 10. A solar collector according to claim 1, wherein said four or more mounting brackets (11 a,11 b,11 c,11 d) are substantially identical to one another.
 11. A solar collector according claim 1, comprising a mounting bracket (11 a,11 b,11 c,11 d), for engaging one or more tube sections of said solar collector, said mounting bracket comprising two tube engaging members (12,13) that can be fixed to engage a tube section in at least two positions, a first position in which the tube section is slidably engaged and a second position in which the tube section is loosely engaged to allow displacement between the tube section and the mounting bracket in a direction transverse to the tube section axis.
 12. A solar collector according to claim 11, wherein at least one of said tube engaging members (12,13) is forked so as to embrace a second tube section that extends transversely from the first tube section.
 13. A solar collector according to claim 11, further comprising a base plate (15) for attaching the mounting bracket to the frame of the solar collector, wherein said base plate (15) is provided with three or more frame facing protrusions (19) to minimize the contact area between the frame and the base plate (15).
 14. A solar collector according to claim 13, wherein through going bores in the base plate (15) coincide with the protrusions.
 15. A solar collector according to claim 13 or 44, wherein the base plate (15) and a first of the tube engaging members (12) are integrally connected to one another by a connecting part (16) that is at an angle with the base plate and the second tube engaging member (13) being securable relative to the first tube engaging member (13).
 16. A solar collector according to claim 15, wherein the connecting part (16) comprises a substantially flat plate section, at least a part of the oppositely disposed free edges (17) of the flat plate section being bent over to reinforce the mounting bracket.
 17. A solar collector according to claim 16, wherein said free edge (17) is bent over to obtain a substantially U-shaped cross-section in which a flat plate part (14) of the second tube engaging member is slidably received.
 18. A solar collector according to claim 17, wherein the flat plate section (14) that is integral with the first tube engaging member is provided with one through going bore (18) and the flat plate part of the second tube engaging member is provided with two through going bores (18) that overlap with the through going bore of the flat plate section in two distinct positions, whereby the tube engaging members (12,13) slidably engage the tube section in one of the two distinct positions and the tube engaging members (12,13) loosely engage the tube section in the other of the two distinct positions.
 19. A solar collector according to claim 18, wherein a pop rivet, bolt or similar fastener is received in the through going bores (18) to fasten the second tube engaging member (13) in either of the two distinct positions.
 20. A solar collector according to claim 11, wherein said tube engaging members (12,13) are at least partially curved with a radius equal to or slightly larger than the tube section to be engaged.
 21. A solar collector according to claim 11, wherein at least a part of the mounting bracket is made of a material with a relatively low thermal conductivity, such as stainless steel, to reduce heat loss via the mounting bracket to the frame. 